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https://issues.apache.org/jira/browse/LUCENE-1536?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13116378#comment-13116378
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Michael McCandless commented on LUCENE-1536:
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bq. I'm definitely +1 to useRandomAccess() but I think there is a usability
question mark around removing getRandomAccessBits(). If we assume that if
DocIdSet.useRandomAccess() returns true then the DocIdSet must be also be a
Bits implementation, then we need to prevent non-Bits implementations from
returning true, or setting true in setUseRandomAccess. If we don't, we're
likely to confuse even expert users because this all comes together in a method
deep inside IndexSearcher.
Well it's quite expert to implement your own random-access filter?
We can fix IS so that if the DIS fails to cast you get a clear exception
stating that useRandomAccess returned true yet the DIS isn't a Bits? Or it
could be silent and fall back to iteration, if the cast fails... but I prefer
the former (so you know your "true" isn't working).
I really don't think we should pollute Bits w/ useRandomAccess method;
random-access is the entire point of the Bits interface. It's too low-level to
push it down there.
And actually having a getter (getRandomAccessBits) is trappy I think, because
the user may not realize it's called for every search and may do something
crazy like allocate a new FixedBitSet every time.
> if a filter can support random access API, we should use it
> -----------------------------------------------------------
>
> Key: LUCENE-1536
> URL: https://issues.apache.org/jira/browse/LUCENE-1536
> Project: Lucene - Java
> Issue Type: Improvement
> Components: core/search
> Affects Versions: 2.4
> Reporter: Michael McCandless
> Assignee: Michael McCandless
> Priority: Minor
> Labels: gsoc2011, lucene-gsoc-11, mentor
> Fix For: 4.0
>
> Attachments: CachedFilterIndexReader.java, LUCENE-1536.patch,
> LUCENE-1536.patch, LUCENE-1536.patch, LUCENE-1536.patch, LUCENE-1536.patch,
> LUCENE-1536.patch, LUCENE-1536.patch, LUCENE-1536.patch, LUCENE-1536.patch,
> LUCENE-1536.patch, LUCENE-1536.patch, LUCENE-1536.patch
>
>
> I ran some performance tests, comparing applying a filter via
> random-access API instead of current trunk's iterator API.
> This was inspired by LUCENE-1476, where we realized deletions should
> really be implemented just like a filter, but then in testing found
> that switching deletions to iterator was a very sizable performance
> hit.
> Some notes on the test:
> * Index is first 2M docs of Wikipedia. Test machine is Mac OS X
> 10.5.6, quad core Intel CPU, 6 GB RAM, java 1.6.0_07-b06-153.
> * I test across multiple queries. 1-X means an OR query, eg 1-4
> means 1 OR 2 OR 3 OR 4, whereas +1-4 is an AND query, ie 1 AND 2
> AND 3 AND 4. "u s" means "united states" (phrase search).
> * I test with multiple filter densities (0, 1, 2, 5, 10, 25, 75, 90,
> 95, 98, 99, 99.99999 (filter is non-null but all bits are set),
> 100 (filter=null, control)).
> * Method high means I use random-access filter API in
> IndexSearcher's main loop. Method low means I use random-access
> filter API down in SegmentTermDocs (just like deleted docs
> today).
> * Baseline (QPS) is current trunk, where filter is applied as iterator up
> "high" (ie in IndexSearcher's search loop).
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